Vitroceramics

ABSTRACT

Translucent and opaque vitroceramics of fine grain and high quality are produced from compositions having 90 percent or more of 4-5 specific oxides with the exclusion of all but minor percentages of other ingredients. The invention describes the raw materials, the composition of the glass from which the vitroceramics are made, and the novel processes by which they are produced.

United States Patent 1191 Tochon Nov. 13, 1973 VITROCERAMICS 3,486,963 12/1969 Smith 106/39 DV [75] Inventor: Jean Paul Tochon, Saint-Cloud, FOREIGN PATENTS OR APPLICATIONS France 986,289 3/1965 Great Britain 106 39 DV Assigneez G b Industries, Great Bl'ltaln Sur Seine France 1,474,487 3/1967 France 106/39 DV 1,471,337 1/1969 Germany 106/39 DV [22] Filed: May 24, 1971 [21] Appl' No; 146,247 Primary ExaminerA. B. Curtis Assistant Examiner-Mark Bell [30] Foreign Application Priority Data ABSTRACT May 26, 1970 France 7019175 Translucent and opaque v1troceram1cs of fine grain 52 us. (:1. 106/39.6, 65/33 and high quality are Produced from Compositions 51 1111. C1. c036 3/22, c036 3/04 ing 90 Percent of more of Specific Oxides With the [58] Field 61 Search 106/39 DV, 39.6 exclusion of but minor Percentages of other ingredients. The invention describes the raw materials, the [56] References Cited composition of the glass from which the vitroceramics UNITED STATES PATENTS are made, and the novel processes by which they are reduced. 3,007,804 11/1961 Kreidl et al. 106/39 DV p 3,205,079 9/1965 Stookey 106/39 DV 10 Claims, 1 Drawing Figure PATENTEU NM 1 3 T973 4 EXOTHERMIC EFFECT TEITPERATURE ENDOTHERMIC EFFECT VITROCERAMICS This invention relates to the industrial production of vitroceramics of high quality and includes new compositions of raw materials, to glasses of novel compositions, to novel vitroceramics, and to novel methods of producing them.

The principle used in the prior art in the manufacture of vitroceramics was to melt glass from a special composition of raw materials, to shape it by one of the ordinary techniques of the glass industry, and to transform the shaped piece more or less completely into polycrystalline material using thermal treatments called ceramization. Those treatments of transformation usually included two essential phases, one called nucleation during which germs or nuclei are formed, and a later phase of crystallization during which these germs are developed into crystals at the expense of the vitreous matrix. The first phase, nucleation, generally occurs at a temperature near the softening temperature of the glass. The crystallization goes forward at higher temperatures.

The manufacture by such known processes of vitroceramic articles which possess simultaneously thermal, mechanical, and chemical properties of high quality could only be obtained by the use of costly raw materials, by raw materials difficult to work with, or by the use of difficult or expensive techniques.

It is an object of this invention to make vitroceramics having mechanical properties such as resistance to bending, to shocks, and to abrasion; chemical properties such as resistance to corrosion and water; and thermal properties such as refractoriness and resistance to thermal shock or high quality, and to make them from industrial raw materials of low cost. Another object is to perfect a process which is better adapted to the rapid and mechanized formation of articles than are the processes of the prior art, which produces products of better qualities, which permits diversification and the production of different vitroceramics for different purposes, and to accomplish these objects by thermal treatments. Other objects of the invention will appear as the description proceeds.

The objects of the invention are accomplished generally speaking by producing from selected, low-cost raw materials a group of glasses of which the composition shown in Table 1 represents at least 90 percent of the total mass of the glass.

TABLE 1 General proportions by weight) Principal constituents In this composition the CaO may be replaced by MgO provided the CaO remains superior to percent, the molar ratio of MgO to CaO remains inferior to 0.15, and the MgO content does not exceed 3 percent by weight of the mass of the glass.

The principal constituents may be derived from common raw materials of the glass industry, silica sand, limestone, dolomite, talc, hydrated alumina, certain blast furnace slags, bauxite, kaolin, and zircon sand. It is also possible to use other natural rocks or industrial by-products always with the reservation that the impurities imported by the raw materials do not exceed 10 percent of the mass of the glass. In particular, the content of Na O and K 0 may not exceed 3 percent of either of them or 4 percent of their total. We have established the fact that the indicated proportion of zirconium oxide plays an essential role in the mechanism of ceramization and is found in certain of the final crystals either in the pure state or in the form of compositions, jointly with other crystals from which it is absent. Among the latter type of crystals gehlenite and anorthite have been identified. Gehlenite has the formula 2CaOAl O 'SiO and melts at l,593C. Anorthite has the formula CaO'Al O '2SiO and melts at l,553C. These crystals have been identified from the work of Levin, Robbins and McMurdie entitled Phase Diagrams for Ceramists but their work was conducted in the absence of ZrO The viscosity of the novel glasses quickly diminishes above the liquidus so that their temperature of fusion and fining remain on the order of l ,500-1,600C. generally attaining as much as l,650C. for the higher contents of alumina.

The novel process, in addition to the novelty of the raw material compositions and the novel composition of the glasses, has a phase of nucleation at temperatures between 850 and 1 C. and a phase of crystallization between 1,000 and 1500C. It is generally advantageous to establish levels of temperature in these phases in order to accomplish them under optimum conditions of speed of nucleation and thereafter of crystallization. The preferred temperatures for nucleation are generally situated between the dilatometric softening temperature of the glass and a temperature inferior thereto by about 5 0C.

The temperature at which the phase of crystallization is carried out is preferably located by less than 100C below the temperature T3 on the accompanying diagram which is the temperature at which the principal crystalline phase resulting from the thermal treatment redissolves into the vitreous phase; the temperature T3 is readily found as the endothermic peak on the differential thermal diagram as illustrated. Nevertheless when it is the object to produce transulcent vitroceramics the temperature of crystallization should be within about 100C. below the temperature T2 in the diagram. The first exothermic peak of crystallization is indicated at T1. The speed at which the temperature of the glass can be allowed to rise during vitroceramization is restricted by the danger of deforming the object being treated; it is therefore useful to use a rate of increase which will avoid deformation, for example 5l0C./- min. for plates lying upon a flat support during treatment. It will be understood that such plates are usually of reasonably uniform thickness and of the order of thickness of the product technically called flat glass.

The cooling of the treated objects may be carried out freely, for instance at the natural cooling rate of a furname of low thermal inertia such as would be employed the structure of the crystals formed may be altered as well as the nature and percentage of the residual phase. Certain generalities can be postulated which will establish for each composition the best treatment for producing special properties, in particular, and as an example compositions of SiO 25-35 percent, A1 40-50 percent, CaO l0-20 percent, ZrQ 8-12 percent will produce translucent vitrocerarnics when the crystallization is carried out at temperatures on the order of l ,lO0C.; whereas the same compositions produce white opaque objects when the treatment of crystallization is on the order of l,300 to 1,450C. l have established the fact that this change in appearance does not result from more complete or finer crystallization but from the formation of different crystalline combinations which produce different physical properties. The invention also provides the possibility of making vitreous products of good mechanical strength, having softening temperatures above l,350C. and fusion points between about l,550 and 1,600C. Such high quality products are produced from glasses made of the composition SiO 25-28 percent, A1 0 38- 44 percent, CaO 20-26 percent, ZrO 9-12 percent by a thermal treatment including short periods of nucleation and crystallization. The nucleation may be carried out at about 900C. for not more than about 30 minutes, the crystallization following between 1,300" and 1330C. for not over 10 minutes.

Another feature of the invention is the production of refractory vitroceramics which are still thermally stable at 1,500C. from glasses having the chemical composition by weight SiO 26-30 percent, A1 0 45-50 percent, CaO 10-l6 percent, ZrO 8-12 percent which are nucleated between 900 and 1,100C. over a period not longer than 3 hours and crystallization between l,350 and 1,500C. for not more than 2 hours.

Considering the temperature levels at which nucleation occurs it is generally advantageous either to adopt a slow rate of temperature increase or to estab lish a period of stable temperature in the nucleation zone.

Generally the properties of the vitroceramics which are produced by the invention are more strongly influenced by the length of the step of nucleation than by its temperature level, and more by the maximum temperature of the level attained during crystallization than by duration of that temperature.

The mechanical resistance of the new products has been determined by the use of a four point circular bending apparatus on parallelepipedic samples 130 X 10 X 4 mm. cut off by a diamond cutting wheel in a plate 10 mm. thick from the vitroceramic under study, the forces being applied to the sawn faces. Thus measured, the mechanical resistance to bending of the new vitroceramics reaches from to 35 kgJmm.

The resistance of the new products to abrasion expressed by a loss of weight in mg/cm was measured by taking a test piece in the form of a cylinder 35 mm. in diameter polished on the face to be tested, and apply ing a rotating disk covered by abrasive paper, silicon carbide grain number 320, with a force of 4 kg. The

loss of weight is determined after 100 turns of the disk, the operation being renewed after replacement of new grinding paper as many times as is necessary to attain a practically constant loss of weight through 10 successive series of 100 turns. The resistance to abrasion is the cumulative loss of weight of these 10 series of 100 revolutions expressed in mgjcm. The figures obtained have generally fallen between 1.4 and 2.7.

The resistance to thermal shocks has been determined upon test pieces 80 X 30 X 5 mm. at C. by plunging them into water at 17C. If the test piece does not exhibit fissures it is returned to the furnace and raised to a temperature 25C superior to the first, that is to say 100C. and so on until it cracks. A very large number of the novel products have been submitted to such tests and have withstood thermal shocks greater than 800C.

Hydrolytic resistance of the new products has been determined by placing l g. of crushed and screened powder of sizes between and microns in a stainless steel beaker containing l00 cc. of distilled water, overlaid by a refrigerant and placed in a constant temperature bath at 999C. The hydrolytic resistance is expressed as the quantity of product which passes into solution in 5 hours, stated as milligrams per gram of product. Under this test the hydrolytic resistance is from 1 to 8 mg./g.

Surface hardness has been measured by a Reichert microdurometer expressed in kg./mrn. The figure corresponds to the weight necessary to force the diamond point into the material until the diagonal of the intaglio measures 10 microns. Measurements are made on a cut and polished surface. The results of these tests on various novel vitroceramics of the invention have yielded figures from 740 to 840.

The softening temperature of the new products is given as the temperature of the first endothermic peak of the curves of differential thermal analysis, of which the drawing gives an illustration. The temperature of this first peak corresponds reasonably to that which can be determined by dilatometry. The results obtained in this or that partial region situated within the general region expressed in Table l are given as illustrations in the following examples but are not to be taken as limitations. In every case the thermal treatments have been carried out in an electrical resistance furnace without precautions with regard to the atmosphere.

EXAMPLE 1 A vitrifiable mixture containing 20.8 kg. of silica sand, 40 kg. oflimestone, 64.4 kg. of hydrated alumina, and 15.2 kg. of zircon sand in each 100 kg. of glass at temperatures of fusion and fining attaining 1,590C. produced the following glass having the composition, expressed in terms of its principal oxides in percent by weight:

Fusion ER 82 i 1 26 A1 0; 42 C210 22 Zr(), 10

Plates of this glass were submitted to different thermal treatments of ceramization as follows:

The vitroceramics produced by these treatments are of fine grain, white color in the mass and lightly ivory in the surface. They have many interesting characteristics of which the principal ones are expressed in the fol- EXAMPLE 2 The raw materials used were of good purity and the following composition:

5 lowmg table sio, A1 0 CaO MgO zro, Na,0 K 0 Products Treated Zircon sand 33.2 0.1 65.7 0.14 Pro erties 82 G 82 H 82 l Bauxite (P56) 7.0 61.45 0.40 0.4 Resistance to bending aolin 46.85 37.6 0.10 0.15 1.98 (Kg/mm 19.2 22.5 34.7 Slag (Senelle) 33.60 15.70 42.35 4.30 1.2 Resistance to abrasion, loss of 1() weight in mgJcm. 2.46 2.07 2.18 S f hardness (kg/mmz) 741 834 The following table compares glass compositions R sistance to herm l h k 800 800 800 containing the essential oxides SiO A1 0 CaO, and g temperature begins ZrO with compositions in which some CaO has been at C. 1350 1350 1350 replaced with MgO. Hydrolytic resistance in 6 6 4 No of MgO/CaO Coefficient of linear dilation Fusion Sioz A1203 cao M80 Z102 moi (X 7) 80 ER 81 26 34 30 10 0 Nature of the crystals principally ER 105 26 34 26 4 10 0.215 ZCaO-ZrO '4810 2 2 ER 176 26342.6 17.8 3.2 10.1 0.20 ER 177 26.2422 19.9 1.6 10.1 0.10 A study of this table reveals the following: The test piece ER 82 H whi h was crystalliz at Plates of these glasses were subjected to ceramization 1,350C. for 6 hours had flexing resistance less than by the following thermal treatments:

Number of Heating Kept Heating Kept the test. t0/iu at/for to/in at/ior Cooling ER 81 sow/a hr..." 900l2 hr 1,300/70 min 1,300/2 hr..-" Free. ER 105... 90073111. !100/2 hr"... 1,250/70 min 1,250/2 hr Do. ER 176. 900731111. 900/1 hr. 1,330/2 hr 1,330/1 hr D0. ER 177... {MOO/3 m1. 000l1 hr 1,330/2 hr 1,330/1 hr D0. ER 82 F now/3 hr D0.

when the temperature is better chosen, as in piece ER 82 1 in which the crystallization was at 1,3 C. and the duration was only 2 hours.

The bending resistance was between 20 and kg./mm. whereas it is on the order of 10 kg./mm. for tempered glass and 7 to 9 kg./mm. for a conventional ceramics of high quality such as those porcelains which are used in electrotechnology.

The resistance to abrasion was between 2 and 2.5 which compares with 1.43 for agate and 5.84 for plate glass.

Surface hardness was between 740 and 840 kg./mm. compared to 880 for agate and to 695 for a sample of flooring stoneware The resistance to thermal shock was 800C. and up which compares favorably with various products of small thermal dilation of which many are much more costly.

Thermal resistance was from 4 to 6 mg./g. whereas it is 12.5 mg./g. for plate glass.

If one uses the glass ER 82 with shorter periods of nucleation and crystallization one obtains the results shown in the following table with excellent properties of mechanical resistance:

Number of Nucleation crystallization resistance to the test Temp. duration Temp. duration bending "C. min. C. min. kgJmm. ER 82 P. 900 10 1330 0 16 ER 82 O. 900 30 1330 0 16.5 ER 82 N. 900 10 1330 10 17.8 ER 82 K. 900 30 1330 10 27 It is to be noted that the value given for the duration of crystallization in ceramics ER 82 P and ER 82 0 means that the program of regulation for the furnace included only the rise in temperature to the maximum indicated, without establishing a period of even temperature, but followed immediately by cooling.

Test 82 F included a test piece of the same composition as those labeled ER 82.

The principal characteristics of the vitroceramics of this example are:

ER 81 ER ER176 ER 177 ER82F Bending resistance (kg/mm?) 12. 3 12 6 17 28. 2 Softening begins about. C.) 1,365 1,330 1,330 1,345

EXAMPLE 3 This example relates to glass ER 172 and ER 173 h g?! co aps t yrly 6 8 er qnt f 2591.

that is to say less than glass 82.

No. of

Fusion SiO A1 0, CaO ZrO, ER 172 26.5 43 22.5 8

Er 173 27 44 23 6 ER 82 26 42 22 10 The thermal treatment used included heating to 900C. in 3 hours, holding at 900C. for 2 hours, heating from 900-l,300C. in 2 hours, and holding at 1,300C. for 2 hours. The glasses had the following characteristics:

ER 172 ER 173 ER 82 Mechanical resistance (kg/mm!) 16.1 14.2 19.6 Softening temperature (C.) 1350 1350 1350 The mechanical resistance of vitroceramics is shown to have been reduced when the concentration of ZrO Raw materials in kg./100 kg. of glass ER 96 ER 116 ER 117 BR 120 15 less than 10 Percent Sand 24.9 22.9 22.9 21.9 Limestone 21.8 29.1 25.4 25 .4 EXAMPLE 4 Hydrated alumina 73.6 70.5 73.6 70.5 5 Zircon sand 15.2 15.2 15.2 18.3 Following the methods of fusion illustrated above, Cerarnization treatments:

Ceramization treatments:

No. of the C001 to .2 Heat. tojin Hold atrfor Heat tofin Hold zit tor 800 C ER $16. 1150 135111; 1.050-1.l00/3 hr IASODJTO min 1.450%? hr" Free. E R 116 9001'3 11L H HOOD/'2 111' 5 L350l90 min. A 1,350/2 hr," Do. ER 117 1100",3l1r. 1100 1? hr 5 5 1,350100 111111.. L350l2 111'. .1 Do. ER 12 .JtltP/d hr 5 A JDl2 hr 1.350;'J0 1ni11 l.35[l.12h11 Do.

and after a thermal crystallization at lower tempera- 15 Properties of the products: ture, a translucent vitroceramic of satisfactory quality was prgducedI Vi troceramics ER 96 ER 116 BR 117 ER 120 initial Softening Raw matenals- Temperature 0) 1500 1510 1515 1525 Sand 24.91 kg./l00 kg. of glass Limestone 21.8 kg./100 kg. of glass Hydrated alumina 73.61 kg./l00 kg. of glass Zircon sand 15.22 kg./100 kg. of glass Temperature of fusion and fining 1640C.

The theoretical composition of the glass (ER 112) was: S10 30 percent by weight CaO 12 percent by weight A1 0 48 percent by weight ZrO 10 percent by weight The thermal ceramization treatments for ER 112E were these: Heat the glass to 900C. in 3 hours; hold at 900C. for 2 hours; heat from 900 to l,l00C. in I hour; hold at 1,100C. for 2 hours; cool to 800C. in 45 minutes.

The vitroceramic had the following characteristics:

Appearance translucent Crystals anorthite Bending resistance- 14 kg.1mrn.

Abrasion resistance-2.7 mg./cm.

Surface hardness 780 ltg/mm.

Hydrolytic resistance- 1.1 mgjg.

Softening temperature begins at 1500C.

The high temperature of softening is to be noted, it being evident that during the measurement of the softening temperature the vitroceramic underwent a new crystallization and that the final vitrocerarnic had altered constitution and properties, particularly in this that the translucent product became opaque.

EXAMPLE 5 Vitroceramic products having an initial softening temperature above 1,500C. can be produced from glasses of which the following compositions, and the preceding ones, are exemplary. The conditions of working and treatment illustrate those which assist in their production. The temperatures of fusion of these glasses are on the order of 1,600 and 1,650C. During ceramization the step of nucleation is between 1,000" and l,l00C. and the step of crystallization between 1,250 and 1,450C. It is to be understood that these values pertain to these particular products and are not limitations:

Compositions of the glasses SiO CaO Al,O;, ZrO, R 30 12 48 10 As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

What is claimed is:

1. A vitroceramic body consisting essentially of at least percent by weight of S10 A1 0 Cao with or without MgO, and ZrO in the following proportions by weight SiO 25-28% A1 0 38-44% CaO 20-26% ZrO 9-1270 MgO, if present, not exceeding 3 percent of the weight of the body and the ratio of MgO/CaO being less than 0.15, and Na O and K 0, if present, not exceeding 3 of either nor 4 percent for both.

2. Strong vitroceramics having a softening point above 1 ,350C. and consisting essentially, by weight, of 810; 25-28 percent A1203 38-44 percent, CaO 20-26 percent, ZrO 9-12 percent.

3. A vitroceramic body according to claim 1, having a softening point at least about 1,350C., containing crystals of pure ZrO and crystals of anorthite, and being opaque and of white color.

4. A vitroceramic body according to claim 1, having a softening point at least about 1,350C., containing crystals of pure ZrO and crystals of gehlenite, and being opaque and of white color.

5. A vitroceramic body consisting essentially of at least 90 percent by weight of S10 A1 0 Cao with or without MgO, and ZrO in the following proportions by weight S102 26-30% A1 0 45-50% CaO l016% ZrO 8-1270 MgO, if present, not exceeding 3 percent of the weight of the body and the ratio of MgO/CaO being less than 0.15, and Na O and K 0, if present, not exceeding 3 percent of either nor 4 percent for both.

6. Highly refractory vitroceramics consisting essentially, by weight of SiO; 26-30 percent by weight A1 0 45-50 percent, CaO 10-16 percent, ZrO 8-12 percent.

7. A vitroceramic body according to claim 5, having a softening point at least about 1,350C., containing 1% cent, CaO 10-20 percent, ZrO 8-12 percent.

10. A white opaque vitroceramic having the composition, by weight, of SlOz 25-35 percent. A120 40- 50 percent, CaO 10-20 percent, ZrO 8-12 percent said constituents constituting at least about percent of its weight.

"5- UNITED S'IA'IES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,77 Dated November 13, 1973 Inventofls) Jean Paul Tochon It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

(3011mm 8; line 63 the second line of claim 6 should read as follows: 1 v

--tia.lly, by weight, of S10 26-30 percent, @1 0 Signed and sealed this 23rd day of April 19714..

(SEAL) Attest:

C I'=IARSHALL DANN Commissioner of Patents ism-man M .FLETCILER JR L, Attesting Officer 

2. Strong vitroceramics having a softening point above 1,350*C. and consisting essentially, by weight, of SiO2 25-28 percent Al2O3 38-44 percent, CaO 20-26 percent, ZrO2 9-12 percent.
 3. A vitroceramic body according to claim 1, having a softening point at least about 1,350*C., containing crystals of pure ZrO2 and crystals of anorthite, and being opaque and of white color.
 4. A vitroceramic body according to claim 1, having a softening point at least about 1,350*C., containing crystals of pure ZrO2 and crystals of gehlenite, and being opaque and of white color.
 5. A vitroceramic body consisting essentially of at least 90 percent by weight of SiO2, Al2O3, Cao with or without MgO, and ZrO2, in the following proportions by weight SiO2 26-30% Al2O3 45-50% CaO 10-16% ZrO2 8-12% MgO, if present, not exceeding 3 percent of the weight of the body and the ratio of MgO/CaO being less than 0.15, and Na2O and K2O, if present, not exceeding 3 percent of either nor 4 percent for both.
 6. Highly refractory vitroceramics consisting essentially, by weight of SiO2 26-30 percent by weight Al2O3 45-50 percent, CaO 10-16 percent, ZrO2 8-12 percent.
 7. A vitroceramic body according to claim 5, having a softening point at least about 1,350*C., containing crystals of pure ZrO2 and crystals of anorthite, and being opaque and of white color.
 8. A vitroceramic body according to claim 5, having a softening point at least about 1,350*C., containing crystals of pure ZrO2 and crystals of gehlenite, and being opaque and of white color.
 9. Translucent vitroceramics consisting essentially, by weight, of SiO2 25-35 percent Al2O3 40-50 percent, CaO 10-20 percent, ZrO2 8-12 percent.
 10. A white opaque vitroceramic having the composition, by weight, of SiO2 25-35 percent. Al2O3 40-50 percent, CaO 10-20 percent, ZrO2 8-12 percent said constituents constituting at least about 90 percent of its weight. 